[Discuss] Port Scanning

[Kent Borg]

I mostly don't like firewalls, seems to me it is better to only listen 
on the ports one wants to listen on and only listen on those for 
specific good reasons. Firewalls are mostly used as a substitute for 
such discipline. Also, iptables rules are a pain to set up, looking more 
prone to error than not.

Until I discovered "ufw" front end: it is actually simple to use! 
(Imagine, a single, simple command to allow a specific inbound port 
number through! What *will* they think of next?) So I used ufw to set up 
some firewalls: but belt-and-suspenders, the firewall as an extra layer 
of protection NOT the only layer of protection.

Which means I now get firewall reports in daily logwatch e-mails.


Anyway, finally to the point.

What is going on in this short excerpt (out of a very long e-mail of 
such stuff):

>     From 103.203.58.1 - 1 packet to tcp(8001)
>     From 103.224.217.31 - 1 packet to tcp(23)
>     From 103.229.127.36 - 1 packet to udp(1434)
>     From 103.237.146.15 - 1 packet to udp(1900)
>     From 103.252.89.123 - 12 packets to tcp(2995,15066,15825,17990,22787,50236,51764,52432,55508,61617)
>     From 104.40.57.205 - 2 packets to tcp(110,2049)
>     From 104.40.57.225 - 1 packet to tcp(26)
>     From 104.40.74.178 - 1 packet to tcp(8888)

Most of it makes sense:

8001: They are looking for a web server on a funny port.
23: THe normal telnet port.
1434: Something MS SQL.
1900: Some UPnP thing.
110, 2049: pop3, NFS.
8888: Probably hoping for a web server again.
26: SMTP on a funny port or some file transfer thing or an old firewall 
(!) or "Dungeon Siege II" game or "W32.Netsky" malware.

But what about that those 12-packets 103.252.89.123 sent to 10 different 
high ports? (note 12 ≠ 10)

Are they really expecting services to be running up there? Are they 
trying to hit return port numbers through a broken NAT? Is that some 
default port-knocking pattern…? They are looking for 10-specific things 
but their script forget that they had already hit two of them? Or two of 
them are two different specific things and hitting those two ports for 
each case was just easier?


Thanks,

-kb


P.S. I do admit that a firewall makes more sense on my daily laptop than 
it does on my servers, because I run a greater variety software on my 
laptop. One day I scanned myself and I discovered it was listening on an 
unexpected port. Turns out I had Rhythmbox was running at the time, and 
it was helpfully defaulting to offering "DAAP Music Sharing". Probably 
not a big problem, but still something I don't want and I turned it off. 
A firewall prevents such accidental things from being accessible. But a 
firewall should not be a primary line of defense, dammit! And I should 
still occasionally scan local host, *and* turn off my firewall and scan 
my IP address(es) from a different machine…

P.P.S. My decades long dislike of firewalls is *finally* getting trendy 
with the impressive name "Zero Trust Architecture", it even has a TLA: 
"ZTA". Nice when the world finally catches up here and there.